This invention relates in general to welding devices and in particular to a new and useful device for feeding the welding wire in a submerged arc welding operation and which includes a support carrying a straightening roller assembly in a position to cooperate with the feeding and straightening of welding wire into association with the welding head comprising tongs formed by a pivotal guide blade and a current carrying blade which are positioned relative to the straightening rollers so as to advance the wire set by the straightening rollers into association with the welding gap formed between workpieces.
The invention relates in particular to a device for feeding the welding wire in submerged arc welding operations in which narrow gap-type joints are to be welded, such as disclosed in German utility model No. 7623758 or German Os No. 26 33 829 (U.S. Pat. No. 4,219,717 to Kuhnan). This device substantially comprises a welding head which is pivotable within a certain angle about an axis which is perpendicular to the welding direction, and is equipped with means for guiding the welding wire in a straight line and for supplying the electric current, and also comprises a wire straightening roller assembly which is connected to the welding head, and a feeder for supplying the welding powder. Narrow gap submerged arc welding is employed at a growing rate for joining thick-walled steel structure elements, particularly in the construction of pressure vessels in nuclear reactors.
The invention is directed to a further development of prior art equipment of this kind, making it possible to weld parts with even thicker walls than hitherto. That is, with the increasing requirement on safety and larger capacities as well as higher pressures of the units, the walls of the vessels, especially of nuclear reactors, become thicker and may reach a thickness of 1,000 mm and even more. Experience has shown that with such extreme wall thicknesses, prior art welding wire feeding equipments no longer satisfy the need. Very high requirements must be placed on the quality and accuracy of location of the weld beads in the narrow gap, to obtain a faultless joint. The thicker the material is, the longer must be the welding head comprising the wire feed blade and the current conducting blade. At the same time, for reasons of economy and metallurgical technology, it is sought not to enlarge the gap, on the contrary, the gap should be narrower if possible, to reduce the zone of welding and thus the welding time. This imposes highest requirements on the geometrical accuracy of the welding wire feed and, consequently, also on the dimensional stability of the blades of the welding head. The requirements on the rigidity of these blades are particularly high if the welding wire supplied thereto is not entirely straight and exerts on the blades a bending force acting transversely to the welding direction and tending to spread the blades apart with the result of affecting their function as guides.